Amplifying system



July 23, 1935. J. H. H MMOND, JR

AMPLIFYING SYSTEM Original Filed Aug. 23, 1930 I v avwentoz 6 E g i; I 33 M elm m Patented July 23, 1935 Q UNITED STATES PATENT OFFICE.

Application August 23, 1930, Serial No. 477,326 Renewed December 16, 1933 12 Claims. (Cl. 179100.1)

This invention relates to amplifying systems and more particularly to an improved system in which the high and low frequency circuits have independent amplifiers but are cross controlled.

The invention relates particularly to a means for separating the high and low frequencies and for amplifying the energy of each in accordance with the strength of the applied signal in both groups.

The invention also consists incertain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which The figure illustrates diagrammatically one type of circuit for carrying out the present invention.

In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring more particularly to the drawing, the figure shows an amplifying system which receives its energy from a phonograph pick up ID, or a photoelectric cell i i. This cell receives light from a lamp 52 which is energized from a source of power 63. The light from this lamp is focused by a lens H through an aperture 95, in an aperture plate it, upon the sound record of a moving film ii. The light which passes through this film then strikes the photoelectric cell N. This cell is connected through a transformer l8 to two contacts 2! of a double-pole double-throw switch 22, the other contacts 23 of which are connected to the phonograph pick up to. The blades of the switch 22 are connected to the primary of a transformer 24, the secondary of which is connected to two filter circuits 25 and .26, the former being a high pass filter, which allows only the upper frequencies to pass, and the latter being a low pass filter which allows only low frequencies to pass. These filter circuits are connected to the primaries of two transformers 21 and 28, the secondaries of which are connected to potentiometers 3| and 32. The potentiometer 3| is connected in the input circuit of a space discharge means 33. The filament of this device is heated from a source of power 34, which also heats the filament of a space discharge means 35. Across the source of power 34 is a potentiometer 36, the adjustable 5 contact of which is'connected through a battery 37? and resistances 38 and 39 in series, to the potentiometer 3i.

The grid of the device 35 is connected through a condenser M to the adjustable contact of the potentiometer 3i, and through a resistance 42 and battery Q3 to the filament circuit.

The potentiometer 32 is connected in the input circuit of a space discharge means M. The filament of this device is heated from a source of power 45 which also heats the filament of a space discharge means 06. Across the source of power 25 is a potentiometer fill, the adjustable contact of which is connected through a battery 48 and resistances 5i and 52 to the potentiometer 32. The grid of the device 46 is connected through a condenser 53 to the adjustable contact of the potentiometer 32 and through a resistance 54 and battery 55 to the filament circuit.

The output circuit of the space discharge means 35 is connected to the primaries of two transformers 56 and El. The secondaries of these transformers are connected through rectifiers 58 and 59 to resistances 39 and 52 respectively. These resistances are shunted by condensers 6| and 62 respectively.

The output circuit of the space discharge means 46 is connected to the primaries of transformers 63 and 64, the secondaries of which are connected through rectifiers B5 and 66 to the resistances 38 and 59 respectively. These resistances are shunted by condensers 61 and 68 respectively.

The output circuits of the space discharge means 33 and M are connected to the primaries of two transformers H and 52 respectively. The secondaries of these transformers are connectd in the input circuits of two amplifiers l3 and 14, the output circuits of which are connected to the moving coil of a loud speaker I5. The field winding 18 of this loudspeaker is energized from a 45 battery TI. 7

In the operation of the form of the invention shown in the accompanying figure, when it is desired to use the phonograph the switch 22 is thrown down, and when it is desired to use the photographic sound record I'l, the switch 22 is thrown up. In either case,'energy is fed to the transformer 24 from the secondary of which it passes to the two filter circuits 25 and 26. The former allows only the high frequencies to pass. 5o

The energy from this circuit passes through the transformer 21 to the potentiometer 3| where any desired amount may be fed to the input circuit of the space discharge means 33. Some of the energy to this circuit passes through the stoppage condenser 4| to the space discharge means The low frequency energy which is allowed to pass through the filter circuit 25, passes through the transformer 29 to the potentiometer 32 where any desired amount may be fed to the input circuit of the space discharge means 44. Some of the energy to this circuit passes through the stoppage condenser 53 to the space discharge means 46.

The output from the space discharge means .35 passes through the transformers 56 and 51 and is rectified by the rectifiers 58 and 59 causing D. C. currents to fiow in the direction of the arrows through the resistances 39 and 52 respectively, thus building up potential differences across these resistances which are proportional to the currents flowing through them and, therefore, to the strength of the high frequency input signal.

The bias on the space discharge means 33 will, therefore, be dependent upon the voltage of the battery 31, the settings of the potentiometers 33 and 3| and the potential differences across the resistances 39 and 3B. Thus, as the currents through these resistances are increased the bias on the device 33 will be decreased, thereby increasing the amplification factor .or gain ratio so that the output of this device will vary in accordance with the input signal strength of both the high and low frequency components.

In a like manner, the bias of the space discharge means 44 will be determined by the voltage of the battery 48, the settings of the potentiometers 41 and 32, and the potential differences across the resistances 52 and 5|. Thus, as the currents through these resistances are increased the bias on the device 44 will be decreased, thereby increasing the amplification factor so that the output of this device will vary in accordance with the input signal strength of both the high and low frequency components.

The output from the devices 33 and 34 will pass through the transformers II and 12 to the amplifiers 13 and 14 where they will be amplified and combined and fed to the loud speaker 15, where the speech or music will be reproduced in a well known manner.

It is thus seen that in this form of the invention the high and low frequency components will be amplified separately, but the amplification factor of each will be dependent upon the signal strength of both of the components so that if, for example, the low frequencies predominate, these low frequencies will be amplified an amount proportional to the input signal strength, and at the same time any high frequencies that may be present will be amplified more than they normally would if they were dependent solely upon the high frequency input signal strength. In like manner if the high frequencies predominate they will also increase the amplification of both the high and low frequencies in a manner similar to that just described.

It will be noted that the above system permits the high frequency currents to pass the amplifier when they are themselves of suflicient strength so that the resultant tone will over-ride the ground noises or scratch and also permits the high frequency currents to pass if the low frequency currents are of such strength that they will mask the high frequency scratch.

The audio frequency tone is split up into high and low frequency sections, each of which is applied to an amplifier having a variable gain ratio and provided with means for controlling the gain ratio in accordance with the input signals. Both the high and low frequency components are ac; cordingly amplified by an amount which is directly proportional to the input signal strength. The low intensity signals are amplified but a small amount, whereas the high intensity signals are more strongly amplified.

The previously mentioned system would prevent the amplification of ground noises such as scratch when unaccompanied with audible signals inasmuch as the signals would be such that the intensity of the scratch tone would be insufficient to operate the amplifier. When an audible signal is applied, however, the amplification factor of the amplifiers is automatically increased and the amplifier is permitted to operate.

By splitting the control in the manner above described so that the high frequency amplifier is controlled in accordance with the signal intensity 1 in the low frequency amplifier as well as the intensity in the high frequency amplifier, the high frequency currents are permitted to pass and are amplified when present in the system by themselves or when accompanied by low frequency signals. I

The same applies to'the control of the low frequency signals either by the intensity of the low frequency signals themselves or by the intensity of the high frequency signals.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes .in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In an audiofrequency amplifier for a sound record, means for separating the signals of high and low frequencies, a separate amplifier for each of said frequencies, means controlledin accordance with the signal strength at each of said frequencies for varying the gain ratio 'of the corresponding amplifier an amount directly proportional to the strength of said signal and means controlled by the signal strength at one of said frequencies for varying the gain ratio of the amplifier for the other of said frequencies di-' rectly as the signal strength whereby one of said amplifiers is controlled in accordance with the signal strength of both the high and low frequency signals.

2. In an audiofrequency amplifier system for a sound record, means for splitting the signal into a high frequency component and a low frequency component, means for separately amplifying each of said components and means controlled by the signal strength for varying the gain ratio of the corresponding amplifier whereby the volume range in the output of each of said amplifiers is expanded with respect to the volume range in the input thereof, and means whereby the signal strength of the low frequency component controls the gain ratio of the amplifier for. the high frequency component whereby the gain ratio 01' said last mentioned amplifier is increased when quency components are present in the system.

3. In a. system of amplifying audiofrequency signals, means for translating a signal from a sound record, a pair of amplifying circuits, filters associated with each of said circuits and connected with said translating means, one of said filters being adapted to pass the high frequency components of the applied signal and the other of said filters being adapted to pass the low frequency components of the applied signal, and means associated with one of said amplifier circuits and controlled by the signal strength in the other of said circuits for varying the gain ratio of the amplifier associated with the former circuit in such manner that the gain ratio is increased when the signal strength in the latter circuit is increased.

4. In a system of amplifying audiofrequency signals, means for translating a signal from a sound record, a pair of amplifying circuits, filters associated with each of said circuits and connected with said translating means, one of said filters being adapted to pass the high frequency components of the applied signal and the other of said filters being adapted to pass the low frequency components of the applied signal, and means for cross connecting said amplifier circuits whereby each of said amplifiers is controlled in accordance with the signal strength in the other of said circuits.

5. In a system of amplifying audiofrequency signals from a sound record, separate amplifying means. for amplifying the high and low frequency components respectively of the applied signal, coritrol means actuated by said components for expanding the volume ratio of the applied signal in each said amplifying means, said control means being cross-connected to said amplifying means whereby the amplification factor of each of said amplifying means is controlled by the signal strength applied to the other of said amplifying means.

6. The method of amplifying an audiofrequency signal from a sound record which comprises separately amplifying the high and low frequency components and varying the gain ratio of the separate amplifiers in accordance with the combined intensity of both components.

7. In an amplification system for audiofrequency signals from ,a sound record, a pair of amplifiers, means for applying the high frequency components of the audio signal to one of said amplifiers and the low frequency components of said signal to the other of said amplifiers, control amplifiers associated with each of said amplifiers and operated in accordance with the high and low frequency signals respectively, and means associated with each of said control amplifiers for controlling the amplification factor of each of said first mentioned amplifiers in accordance with the strength of signal applied thereto.

8. In an amplification system for audiofrequency signals from a sound record, a pair of amplifiers, means for applying the high frequency components of the audiosignal to one of said signal strength applied to either of said control amplifiers.

9. In an amplification system comprising a pair of variable impedance amplifiers having control elements, .a soundrecord, a sound pick up device for said record, means for separating the high and low frequency components of said sound and applying the same selectively to said amplifiers whereby said components are separately amplified, and means for varying the potential of' said "control elements in accordance with the averagesignal strength of either the high or low frequency signals in such manner that said amplifiers are rendered substantially inoperative except when signals are present in the input circuit of one of said amplifiers, the arrangement being such that ground noises and scratch are not amplified when unaccompanied by desired signals. 7

10. In an'audio frequency amplifier for a sound record, means for separating and separately amplifying selected components of a signal, control means actuated by each of said components, and means whereby said control means automatically varies the amplification factor of each said amplifying means so that the amplification factor of each of said means is governed by each of the said components.

11. In a translating system for sound records, a pick-up device, a pair of parallel audio-frequency circuits, dividing means for dividing the audio-frequency signals picked up by said device and feeding said divided signals to said pair of circuits, a combining circuit for recombining said signals, a translating device fed thereby, and a control circuit fed by one of said parallel circuits at a point between said dividing means and said combining circuit for controlling the transmission characteristics of the other of said parallel circuits. 7 1

12. In a sound reproducing system for use with a sound record, a pick-up device, a pair of parallel audio-frequency circuits, dividing means for dividing the signals picked up by said device and feeding said divided signals to said pair of circuits, a combining circuit for recombining said signals, aloud speaker fed thereby, and a control circuit fed by one of said parallel circuits at a point between said dividing means and said combining circuit for controlling the transmission characteristics of the other of said parallel circuits.

JOHN HAYS HAMMOND, JR. 

